Protein Phosphorylation in Response to Diverse Mitogenic Agents in Dog Thyroid Cells
Among the variety of changes induced upon addition of growth factors to quiescent cells are changes in the phosphorylation of cellular proteins which occur rapidly. The receptor molecules for epidermal growth factor (EGF), and for platelet derived growth factor (PDGF) and insulin, have been shown to contain an inherent, growth factor-dependent tyrosine protein kinase activity that was first identified in association with certain viral transforming proteins. In addition, protein kinase C has been reported as a receptor protein for tumor promoters, such as tetradecanoyl-phorbol-acetate (TPA), that stimulate the kinase activity. A rapid tyrosine-specific phosphorylation of two proteins of 42K is observed in fibroblasts of several species stimulated to proliferate in a variety of ways: growth factor induction, trypsin treatment, exposure to phorbol esters and ASV transformation. It has been suggested that phosphorylation of these 42K proteins might be important in the pathway leading to the mitogenic response.
KeywordsProtein Phosphorylation Phorbol Ester Alkali Treatment Thyroid Cell Mitogenic Response
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